#FREE PASCAL UNITS CODE#

The memory for this variable is allocated on the stack when the program executes the routine defining it. The scope of the identifier spans the whole procedure, including nested routines (unless an identifier with the same name in the nested routine hides the outer definition). Local variables: If you declare a variable within the block defining a routine or a method, you cannot use this variable outside that procedure.You cannot use an identifier outside its scope. The basic rule is that an identifier is meaningful only within its scope-that is, only within the block in which it is declared.

#FREE PASCAL UNITS CODE#

The scope of an identifier (such as a variable, procedure, function, or a data type) is the portion of the code in which the identifier is accessible. (In fact, as we’ll see in the next chapter, the effect of the private keyword is related to the scope of the unit containing the class.) In Pascal, units are the key to encapsulation and visibility, and they are probably even more important than the private and public keywords of a class. You can continue to have traditional units, with functions and procedures, and you can have units with classes that do not refer to forms or other visual elements. However, containing form definitions is certainly not the only use for units in Delphi. Delphi automatically places a new class data type in a unit each time you create a form. In Delphi applications, the data types are probably used the most often. The interface of a unit can declare a number of different elements, including procedures, functions, global variables, and data types. The units you refer to can be both in source code format (PAS) or compiled format (DCU), but the compilation must have taken place with the same version of the Delphi. The implementation portion of the unit is considered only when that unit is compiled. The effect of a uses statement is to import just the precompiled interface portion of the units listed. All the units you refer to must be present in the project directory or in a directory of the search path (you can set the search path for a project in the Directories/Conditionals page of the project’s Options dialog box).Ĭ++ programmers should be aware that the uses statement does not correspond to an include directive. When you need to refer to other units from the code of the routines and methods, you should add elements in this second uses clause instead of the first one. The second uses clause, at the beginning of the implementation section, indicates more units we need to access only in the implementation code. This includes the units that define the data types we refer to in the definition of other data types, such as the components used within a form we are defining. The uses clause at the beginning of the interface section indicates which other units we need to access in the interface portion of the unit. Initialization // optional initialization part finalization // optional clean-up code end. all the exported functions must be coded procedure MyProc īegin //. list of exported functions and procedures procedure MyProc Interface // other units we need to refer to uses The general structure of a unit, with all its possible sections, is the following:

Finally, the unit can have an optional initialization section with some startup code, to be executed when the program is loaded into memory it can also have an optional finalization section, to be executed on program termination. A unit has a unique name corresponding to its filename, an interface section declaring what is visible to other units, and an implementation section with the real code and other hidden declarations.

This blank unit contains the following code, delimiting the sections a unit is divided into: By selecting the File > New menu command and then the Unit icon in the New page of the Object Repository, you add a new blank unit to the current project. Units do not need to define forms they can simply define and make available a collection of routines. When you add a new form to a project (with the corresponding toolbar button or the File > New Form menu command), Delphi actually adds a new unit, which defines the class for the new form.Īlthough every form is defined in a unit, the reverse is not true. In a Delphi application, every form has a corresponding unit behind it. Units, in fact, were the basis of the modularity in the language before classes were introduced. The cover of the 4th edition of Essential Pascal,ĭelphi applications make intensive use of units, or program modules.

Free pascal units